1. Technical Field
The present invention relates to a process for protecting surfaces prone to corrosion by applying a composition that has a relatively high content of unreacted polyisocyanates.
2. Prior Art
Traditionally, it has been problematic to paint directly over rust. Merely painting over rust generally traps moisture and oxygen under the paint, which chemicals continue to corrode the underlying steel surface. Ordinarily, rust must be mechanically or chemically removed before coating. Mechanical methods include sandblasting and applying steel wool. One chemical method is acid treatment.
Various claims have been made about xe2x80x9crust converters.xe2x80x9d For example, phosphoric acid converts iron oxide to an iron phosphate complex. Latex compositions have been alleged to convert the rust to magnetite. Still other products claim to convert rust to iron stearate, iron rosinate and other iron compounds. These products have varying degrees of effectiveness. However, the products may not last long or require a topcoat, after which the coating still does not last very long.
Aluminum pigments are used widely in coatings as special-effect pigments. The term special-effect pigments is used to denote pigments which have a directed reflection at oriented, metallic or highly light-refractive particles of a predominantly flat configuration. They are always of plate-like or flake-like configuration and have very large particle diameters compared with dye pigments. Their optical properties are determined by reflection and interference. Depending on transparency, absorption, thickness, single-layer or multi-layer structure, the special-effect pigments exhibit a metallic shine, a pearl shine, interference or interference reflection. The main areas, of use are in the cosmetics and automobile sectors, in addition in coloring plastic materials, paints, leather coatings, in printing and ceramics.
What is needed is an easy-to-apply coating that simultaneously dehydrates the rust and seals the rust from future oxygen or water attack.
A method of protecting surfaces from corrosion is disclosed herein. In one embodiment, there is provided a method of protecting surfaces from corrosion, which provides a coating composition containing polyisocyanates with unreacted, active NCO groups. The coating composition is applied to a rust covered surface, whereby the active NCO groups in the coating composition react with the water within rust to dehydrate the rust and produce a strong coating with the underlying iron or steel which keeps out water and oxygen which corrode surfaces. In another embodiment, the active NCO content is about 3% to about 20%. In yet another embodiment, the active NCO content is about 5% to about 15%. In another embodiment, the active NCO content is about 5% to about 15%.
Also disclosed is a composition for coating an iron surface, the composition comprising polyisocyanates whose NCO content is between 5% and 20% and whose aluminum flakes are about 5% to about 50% by weight. In another embodiment, the NCO content is between about 7% and about 25%. In another embodiment, the NCO content is between about 10% and about 20%, between about 10% and 20%, or between about 12% and about 18%. The aluminum flake content is about 7% to about 40%, or preferably between about 10% and about 30%.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.